Summer School?

Summer has long been my favorite season, not least because it meant summer vacation for many years. In those days of yore, school stayed in session until mid-June and didn’t resume until after Labor Day. (In fact, my college was on the quarter system, and school didn’t resume until late September.) Does anyone know why school (in large swaths of the country) now ends in early May and resumes in mid-to-late August? It doesn’t make sense to me because (1) there’s still cool, rainy weather in May, (2) there’s still a lot of summer left after school resumes, and (3) taxpayers must be paying for a lot of extra air-conditioning as a result of (1) and (2).

There are explanations for this idiocy (e.g., here), but I find them unpersuasive and rather like explanations of how the tail wags the dog.